Materials Science and Engineering B49 (1997) 243 – 246 Letter Bridgman growth of GaSe crystals for nonlinear optical applications N.B. Singh a, *, R. Narayanan b , A.X. Zhao b , V. Balakrishna a , R.H. Hopkins a , D.R. Suhre a , N.C. Fernelius c , F.K. Hopkins c , D.E. Zelmon c a Science and Technology Center, ESSD, Northrop Grumman Corporation, 1350 Beulah Road, Pittsburgh, PA 15235, USA b Department of Chemical Engineering, Uniersity of Florida, Gainesille, FL 32611, USA c Materials Directorate, Wright Laboratory, Wright -Patterson AFB, OH 45433, USA Received 8 May 1997; received in revised form 9 August 1997; accepted 9 August 1997 Abstract We have grown and fabricated single crystals of gallium selenide for nonlinear optical applications in the mid-infrared wavelength region. A numerical method involving the finite volume technique was used to optimize the crystal growth furnace configuration. Crystals were grown using the liquid encapsulated Bridgman method in a vertical geometry. The modified crystals grown in the optimized furnace temperature profile showed a second harmonic conversion coefficient (d ) which was higher than that of pure GaSe crystals. © 1997 Elsevier Science S.A. Keywords: Bridgman crystal growth; GaSe crystals; Nonlinear optical crystals 1. Introduction There is a strong need of nonlinear optical crystals to cover near-infrared and far-infrared wavelength re- gions. Many attempts [1,2] have been made to commer- cialize several materials but so far no material has clearly demonstrated systems applications. Gallium se- lenide (GaSe) is an excellent material [3,4] for frequency conversion application in a wide transparent wave- length region. It transmits between 0.65 and 19  m without any absorption band. Its application in com- mercial systems is hampered by its strong cleaving tendency perpendicular to the c -axis. We have developed a liquid encapsulated Bridgman crystal growth method to grow modified (doped) GaSe which has shown much better fabricability compared to pure GaSe. The growth process involves both concen- tration and temperature gradients; these in turn cause density gradients and hence convection results under l-g conditions. Convection is generally undesirable as the dopant is carried to the solid–liquid interface and is thus impregnated into the solid matrix. Microgravity experiments help in reducing both thermal and solutal convection if proper precautions are taken to account for random accelerations during crystal growth in space. In a systematic study to achieve large fabricable GaSe we have used a numerical method to optimize the furnace configuration. This method involves finite vol- ume techniques. We have grown, fabricated, and mea- sured the d coefficient for pure and modified GaSe crystals and preliminary results are reported in this paper. 2. Experimental method 2.1. Preparation of mixture: A gallium selenide mixture was prepared by mixing as-supplied Ga (6–9’s pure) and Se (6–9’s pure), and * Corresponding author. Tel.: +1 412 2561469; fax: +1 412 2561661. 0921-5107/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S09 21- 5 1 07(97)00 1 37 -2